class interval

14 LETTERS · STARTS WITH C

class interval is a valid 14-letter word worth 18 points in Scrabble and 23 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

C3L1A1S1S1I1N1T1E1R1V4A1L1

3 + 1 + 1 + 1 + 1 + 0 + 1 + 1 + 1 + 1 + 1 + 4 + 1 + 1 =18 PTS

DOUBLE WORD → 36TRIPLE WORD → 54

MEANING

What does class interval mean?